In recent years, environmental regulations imposed on electrical appliances such as information apparatuses (for example, laptop personal computers) have become stricter. The EuP Directive (Directive on Eco-Design of Energy-using Products) was established and put into effect in the EU member countries. According to the EuP Directive, information technology equipment is required, by the year 2013, not to consume power exceeding 0.5 W in a standby mode and an OFF mode while the equipment is connected to the commercial power supply. A laptop personal computer (it will be hereinafter referred to as “laptop PC”) has an on-board battery pack, operates on the power supplied from the battery pack while being operated outside the office, and operates on the power supplied from the commercial power source through an AC/DC adapter while being operated inside the office.
When an AC/DC adapter is connected to a laptop PC equipped with a battery pack, the AC/DC adapter simultaneously supplies charging power for the battery pack and power for operating the system. The laptop PC, even in a power-off state, needs to supply a part of devices therein with a specific amount of power. The laptop PC, in the power-off state, provides different services or functions between a state in which the AC/DC adapter is connected (it will be hereinafter referred to as “AC power supply”) and a state in which the AC/DC adapter is not connected (it will be hereinafter referred to as “DC power supply”).
When the laptop PC is in the power-off state on DC power supply, the power consumption can be small. This is because the supply of power is limited to that required only for those circuits necessary for use in restart, so that the battery consumption may be prevented as much as possible. However, when the laptop PC is in the power-off state on AC power supply, the power consumption must increase because various services must be provided. First of all, a circuit that operates to monitor the state of the battery and to charge the battery must consume power because a battery charger is activated and charges the battery pack when needed even in the power-off state.
Next, when a Wake-On-LAN (WOL) function for remotely starting the laptop PC is enabled, a circuit that operates to receive a startup packet and to start the laptop PC must consume power. In addition, when charging of a USB device connected to the laptop PC is supported in the power-off state, a circuit operative for charging the USB device consumes power. Further, for the purpose of providing user-friendliness, power is also consumed by a circuit operative for displaying a connection state of the AC/DC adapter, a charging state of the battery pack, a power state, and the like, and by a circuit operative for starting the laptop PC in compliance with the power state. For this reason, the laptop PC tends to consume a relatively large amount of power even when it is in the power-off state on AC power supply.
Japanese Patent Application Laid-Open No. 2004-192350 discloses a method for reducing standby power when a computer device equipped with a battery is shut off while being connected to AC power. According to the charging method disclosed in the document, when power is turned off while the device is connected to the AC power, a so-called M power supply system that realizes a charging function is temporarily turned off and turned on thereafter when a predetermined time counted by a timer elapses, and the charging condition of the battery is checked. If it is determined that charging is necessary, the battery is charged up, and the M power supply system is turned off again. The document also describes that, when the device is turned off while being connected to the AC power, unnecessary devices connected to the M power supply system and a wakeup function are turned off by settings implemented by software.
Japanese Patent Application Laid-Open No. 2009-278288 describes when a LAN cable connected to a server is connected to an Ethernet (controller, a CPU automatically recognizes the server, and saves a user from performing an operation to make the CPU recognize the server. The same document also discloses that, when the Ethernet controller detects that the LAN cable is connected to a LAN jack, the CPU is interrupted and notified of this fact.
Japanese Patent Application Laid-Open No. 2010-33519 discloses a printer with a plurality of interfaces (I/Fs) including a USB interface and is capable of automatically changing the I/F by detecting the connection of a USB cable. The same document describes that, when the printer is connected to a host computer through a USB cable, a USB connection detector of the printer detects that the USB cable is connected by sensing a change of the potential of Vbus.
Japanese Patent Application Laid-Open No. 2009-199297 describes that when PCIe slots connected to a PCIe-PCIe bridge are all detected as not being mounted with cards, a DC/DC converter provided for exclusive use of the PCIe-PCIe bridge is controlled so as to stop supply of power to the PCIe-PCIe bridge.
In the method of Japanese Patent Application Laid-Open No. 2004-192350, since the M power supply system is operated to supply power to the circuit for monitoring the charging state of the battery when the predetermined time elapses after turning of the power off, it might be possible to reduce the standby power for a period during which the M power supply system is not in operation. However, there is a case where the M power supply system cannot be stopped when the M power supply system is operated to serve as a power supply for the other services. Particularly, according to a specific program for electric power saving, the ENERGY STAR program for electrical appliances promoted by the United States Environmental Protection Agency, business' computers must have the WOL function enabled in principle. In addition, depending on the business, users are required to always enable the WOL function. In such a case, the M power supply system is unable to be stopped according to adoption of the method of Japanese Patent Application Laid-Open No. 2004-192350. ENERGY STAR is a registered trademark of the U.S. Environmental Protection Agency in the United States.
Further, if it is necessary to support charging of any USB device connected to a laptop PC in a power-off state, the M power supply system cannot be turned off unless another new power supply circuit different from the M power supply system is provided. Consequently, it is not possible either to reduce the standby power on AC power supply to a level fulfilling the requirements under the EuP Directive or to charge the USB device only by the method of Japanese Patent Application Laid-Open No. 2004-192350. Since the operating system (OS) and device drivers are not operating in the power-off state, it is not easy to determine whether or not an operation of the M power supply system is necessary. Therefore, it is necessary to adopt special measures.